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A small, little-known planet beyond Pluto appears to have an atmosphere, Japanese astronomers announced Monday, challenging previous beliefs about icy objects in our cosmic neighborhood. If verified, this approximately 310-mile-wide (500-kilometer) body would be only the second object beyond Neptune in our Solar System known to sustain an atmosphere—after Pluto.
Once considered a planet, Pluto was reclassified as a dwarf planet in 2006, partly due to the discovery of similar objects in the distant Kuiper Belt. Although NASA, under former President Donald Trump’s administration, has suggested the possibility of reinstating Pluto’s planetary status, the detection of an atmosphere on this nearby object may weaken that argument.
The discovery was made by Japanese scientists and an amateur astronomer who focused their telescopes on an object called (612533) 2002 XV93. This icy world orbits almost 40 times farther from the Sun than Earth—about six billion kilometers away. These distant, dark bodies can only be observed when they pass in front of a distant star.
During a stellar occultation in January 2024, the team noted that the star’s light did not reappear immediately, implying that a thin atmosphere was filtering the star’s light. They estimate that this atmosphere is five to ten million times thinner than Earth’s, according to a study published in Nature Astronomy.
Lead researcher Ko Arimatsu from Japan’s National Astronomical Observatory explained, “This is significant because, until now, Pluto was the only trans-Neptunian object confirmed to have an atmosphere.” Such small celestial bodies were previously thought incapable of hosting any atmosphere.
“This discovery challenges the conventional understanding that small icy worlds in the far reaches of the Solar System are mostly inactive and unchanging,” Arimatsu added.
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